Interactive television (TV) systems are known from for example U.S. Pat. No. 5,233,654. Interactive television systems typically involve the transmission of programming and/or control data (hereafter PC-data), as well as audio and video information, to respective receiving apparatus. The receiving apparatus decodes the PC-data, and applies it to some type of control apparatus for automatic use by the receiver or selective use by the user of the receiver. The control apparatus may take the form of a computer, for example, and the use may include downloading selective e.g., financial data for subsequent user manipulation.
As envisioned herein, information in the interactive television system (ITVS) is transmitted in compressed digital form. The receiving end of the system includes an integrated receiver decoder (IRD) for receiving and decompressing the transmitted information and providing decoded audio, video and PC-data to respective processors. The audio and video processors may be audio and video reproduction devices or a television receiver and the PC-data processor may be a computer. Ideally the system will only provide well tested PC-data provided by authorized service providers, and under such conditions there is little likelihood of transmitted information actually damaging respective receivers. However, if a large number of service providers are authorized to use the system, it becomes vulnerable to a) invasion by unauthorized users and intentional infliction of damage to system users, and b) careless preparation of PC-data and consequent unintentional damage to system users. The ability to broadcast PC-data to tens of thousands of IRD's simultaneously, multiplies the potential disruption that may be inflicted by ill behaved software many fold. Thus there is a need for measures to assure protection of respective ITVS receivers from both ill behaved and unauthorized PC-data.